Found my HP problem

[Ccmano]

After doing all the usual upgrades on my engine, Ported top end, chip, SW headers, modified corsa, new injectors, HO coils etc. I had the car dyno'd a couple weeks ago and was somewhat disappointed the get HP/Torque readings of 369/370. While the torque reading is good, the HP output is about 20 lower than expected. While there are alot of variables I suspected I knew what the problem was.

After all the mods were done I felt the Corsa system was too loud for my taste. I had a local exhaust shop swap out the corsa resonator for an X-pipe and a magnaflow resonator. I loved the sound and was happy till the dyno run. I finally jacked the car up and crawled under to take a look at their work today. What I didn't realize is that for some reason the shop used 2" pipe between the x-pipe and the resonator and between the resonator and the connection to the 2.5" Muffler pipes. This meant I had a system with a 3" header collector into 3" HF Cats into a 2.5" x-pipe into 2" pipe into a 2.5" resonator into 2" pipe into 2.5" mufflers. Not condusive to good flow.

It just goes to show you if you want things done right you have to do them yourself and inspect the work others do for you before you accept it.

The resonator and 2" pipes will have to come out. Since the corsa system is a 2.5" system I will leave the 2.5" x-pipe. I'm thinking of using a Borla resonator. The Corsa resonator is nothing more than straight pipe with an expansion chamber. It looks like the Magnaflow resonator that was used has pipe spacing that is too far apart. I need a resonator with a bit more muffling ability than the Corsa and that aligns correctly with the pipes. Given that I want it quieter I will have to give up some HP. But 20 is more than I am willing to give.

Other than the Borla resonator any thoughts on what to use in there?

H

[LGAFF]

You should through the exhaust from my 92 on it while its off the car and head to the dyno

I would call Mike at twisted....he used 3' stainless on my car and I am sure he would change it....is the 2" what the kit came with?

[LGAFF]

Only bad thing about the Borla is its 2.25 neck down as it enters the resonator

[rhipsher]

I'm doing all of the same mods you did right now. I don't want to set myself up for dissapointment by having expectations of big dyno #'s. I've got a Borla exhaust system right now and like the sound of it. It may not be the best exhuast performance wise but after top end porting and Jeal headers and tuning we will see. I have no idea what to expect from it all. I just hope it puts a smile on my face.

[Paul Workman]

Originally Posted by Ccmano

Other than the Borla resonator any thoughts on what to use in there?

H

Wow! Talk about restriction and all manner of reflections! Sheesh! But, I'm glad to hear ya found it.

As for noise, I have a Borla resonator, if you want to try it.

I just finished hanging my 3" system under my Z today. It still needs some regulating to get it all aligned right. Soon as I can arrange it, I'm also going to add the "Power Stick" 18" mufflers in place of a resonator (behind the SW crossover), and then going thru the Maganaflow twin tube mufflers. It will be a true 3" all the way to the muffler inlet that does shrink down to 2.5. But, I don't think a restriction that far back is going to result in much loss. Certainly it is better than the obstruction in the B&B mufflers.

I don't mind a little noise, but don't want to have to shout to carry on a conversation while in cruise mode.

I'll let y'all know how it works out.

P.

[-=Jeff=-]

Originally Posted by LGAFF

Only bad thing about the Borla is its 2.25 neck down as it enters the resonator

Actually... it necks down worse then that

I would say buy the X pipe resonator form Paul.. it is the magnaflow set up.. that would be better

[xlr8nflorida]

You should be at 450 or 400 RWHP with your setup.

The exhaust is hurting some but not that bad. I have borla on my car and I'm probably leaving 10HP on the table over a B&B system. Mine sounds alittle throaty but more like a sleeper - I prefer that over a bunch of resonance.

[tomtom72]

Hans, is the top end P & P including head porting and re-degreeing of the cams?

I'm asking as your dyno numbers are exactly like a 90 that I inquired about. He had a P&P to the plenum and I/H's and a chip and headers w/o cats. The P&P and chip was mail order from Mr. Haibeck's shop and the owner did his own assembly work. His heads & cams were not touched, and his dyno sheets which he posted in his add were right at a 365 hp avg for three runs. I don't remember the brand of headers and the exhaust.......it was a long time ago.


Tom

[Paul Workman]

Originally Posted by tomtom72

Hans, is the top end P & P including head porting and re-degreeing of the cams?

I'm asking as your dyno numbers are exactly like a 90 that I inquired about. He had a P&P to the plenum and I/H's and a chip and headers w/o cats. The P&P and chip was mail order from Mr. Haibeck's shop and the owner did his own assembly work. His heads & cams were not touched, and his dyno sheets which he posted in his add were right at a 365 hp avg for three runs. I don't remember the brand of headers and the exhaust.......it was a long time ago.


Tom

365 at the wheels??? Somethin' ain't right!! Mine dyno'ed last fall at 339 stock (except for a Borla cat-back). I don't know what it is at now - soon to find out - but w/ top end porting and Marc H's chip, and not changing the stock exhaust, turned my 90 into a whole new animal! I would think it should be between 390 and 400...NOT 365, if the dyno graphs posted on Marc's wall are any indication.

[tomtom72]

Yea, Paul. The other thing that I don't recall for sure was the brand of dyno....I think it was Dyno-Jet?

But it's what this 90's numbers were. This was when I was looking for a Z to buy, I was a noob so I knew very little about any of the finer points on our cars. This guy was generous in that he took the time to give me some heads up on what I should be buying in a used Z.


Tom